1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine or printer, and to be detailed further, relates to an image forming apparatus capable of forming an image with a plurality of colors.
2. Description of Related Art
Simultaneous multicolor copying machines have been developed which can form an image wherein both sides of a boundary preliminarily selected in the direction of scanning an original document are colored differently by one copying operation. This is such that, for example, means for selecting the position for changing of the image color such as a sliding type editing lever is disposed on a document table, and a plurality of developing devices are changed-over selectively with this position of change-over set as a boundary, and thereby an image is formed with different colors by individual colors of the developing devices.
On the other hand, copying machines have been put in practical use which, in addition to such a copying function, have a function that when a original document of plural sheets one side of which is bound such as a book, is copied, it is placed on a document table with both pages opened, and a copy corresponding to each opened page is produced in a split manner one by one page, or a copy is produced on the both sides of one copying sheet.
Then, where change-over of the image color is performed in copying a book in the above-described copying machine, for example, for a book whereto indexes are affixed such as a reference book, it is requested that this index portion, that is, each portion of the right and left ends of the both opened pages is formed into an image of a different color. In such a case, when one editing lever is mounted, only position of change-over for one page can be selected, and in copying, the other page is formed into a monochromatic image. For this reason, it is considered that the position of change-over is selected again, and copying is performed twice, but this method cannot make the most of the copy editing function for books, being inefficient.
Then, it is considered that two editing levers are disposed and two positions of change-over are selected, but this method is expensive in cost in comparison with the method using one lever, and it is required that the position of change-over is selected for each page despite that the right and left pages are of the same form, and therefore this method is inefficient and the operation thereof is complicated like the former method.
Also, for example, where the book as described above is disjointed into sheets of double-side document, and the double-side document is copied on the both sides of one copying paper with the index portion color-identified like the above case, a desired copy cannot be obtained unless the position of the change-over of the rear surface is changed after completing the copy operation of the surface. Particularly, where an automatic document feeder is used, it is impossible to change the position of change-over before copying the rear surface, and the problem exists that for the rear surface, a portion other than the index portion is color-identified.